Rare earth activated hafnium phosphate luminescent materials

ABSTRACT

Luminescent materials having an Hf3(PO4)4 host with an activator selected from the group consisting of terbium, praseodymium, dysprosium, thulium and europium. Color emission varies from red through blue depending upon activator. Excitation radiation includes one or more of cathode rays (CR) long and short wavelength ultraviolet (U.V.) and x-ray. The phosphors are prepared by firing in open crucibles a homogeneous mixture of suitable compounds to yield the phosphor.

United States Patent 11 1 [111 3,905,912 Mathers Sept. 16, 1975 [54]RARE EARTH ACTIVATED HAFNIUM 3,600,324 8/1971 Bril et a1 252/301.4 PPHOSPHATE LUMINESCENT MATERIALS 3,609,094 9/1971 Shaffer 252/3OL4 P [751Inventor: James E. Mathers, Ulster, Pa. Primary Examinermlack Cooper[731 Assignee: GTE Sylvania Incorporated, Attorney, Agent, or FirmNormanJ. OMalley;

Stamford, Conn. William H. McNeil]; Donald R. Castle [22] Filed: Sept.25, 1974 21 App]. No: 509,289 [57] ABSTRACT Luminescent materials havingan Hf (PO host with 52 us. c1. 252/3014 P; 252/3014 F 1 actwatorseleited fmm thegmup i blum, praseodymlum, dysproslum, thulium and euro-2 is f; pium. Color emission varies from red through blue de- 1 1e 0care pending upon activator. Excitation radiation includes one or moreof cathode rays (CR) long and short [56] References Cited wavelengthultraviolet (U.V.) and x-ray. The phos- UNITED STATES PATENTS phors areprepared by firing in open crucibles a homo 2,427,728 9/1947 Jenkins eta1 252/3014 P geneous mixture of suitable compounds to yield the3,488,292 1/1970 McAllister 252/3014 P h h 3,527,710 9/1970 Toma et a1.252/301.4 P 3,586,637 6/1971 Blasse et a1 252/301.4 P 5 Claims, N0Drawings RARE EARTH ACTIVATED HAFNIUM PHOSPHATE LUMINESCENT MATERIALSBACKGROUND OF THE INVENTION This invention relates to luminescentmaterials of the type known as phosphors. More particularly, it relatesto phosphors having an I-lf (P host and a rare earth (RE) activator.

It would be an advance in the art to provide a family of phosphorshaving a wide range of color emission and a wide range of energizingradiation.

OBJECTS AND SUMMARY OF THE INVENTION It is an object ofthis invention toprovide such a family of phosphors.

It is yet another object of the invention to provide a method of makingsuch phosphors.

These objects are accomplished in one aspect of the invention by theprovision ofa family of phosphors having as host I-I 3(PO with arare-earth activator se lected from the group consisting of terbium,praseodymium, dysprosium, thulium, and europium. The color gamut willrange from red to blue depending upon activator.

The phosphors are prepared by forming mixtures of a suitable hafniumsource, a suitable phosphate source, and a suitable RE source, and thenfiring for a sufficient time at a suitable temperature to form thephosphor. The firing takes place in open crucibles.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding ofthe present invention,

together with other and further objects, advantages,

and capabilities thereof, reference is made to the following disclosureand appended claims.

Referring now to the invention with greater particularity, there areherein provided Hf3(PO,) host phosphors having as an activator fromabout 0.05 to 0.10 mole of a rare-earth selected from the groupconsisting of terbium. preseodymium, dysprosium, thulium, and europium.

These phosphors can be prepared ny heating mixtures of suitable sourcesof hafnium, phosphate, and RE. Such suitable sources for hafnium and theRE can be, for example, oxides, oxychlorides, hydroxides, basiccarbonates, oxalates, or nitrates. The phosphate source can be eitheracid or oxide phosphorus compounds. Preferably, the compound is one ofthe ammonium phosphates.

The following non-limiting examples are exemplary. It should further berecognized that the starting materials used should be of the higherdegree of purity which is recognized in the art to be necessary for thepreparation of luminescent materials.

EXAMPLE I The following materials:

63.1 g hafnium dioxide (HfO 52.8 g diammonium hydrogen phosphate [(NH1.87 g terbium oxide (Tb O are intimately mixed together to form asubstantially homogeneous mixture. This mixture is then heated for fourhours at 1,300C in an open crucible. When cool, the phosphor product, Hf(PO Tb, emits a bright yellowish-green when excited by 2537A U.V.radiation; 3,650A U.V. radiation and CR.

EXAMPLE II The following materials:

63.1 g HfO 52.8 g (NHJ HPO 1.70 g Pr O are mixed and treated as inExample I. The phosphor product emits red when irradiated with CR.

EXAMPLE III The following materials:

63.1 g HfO 52.8 g (NHQ HPO 0.933 g Dy O are mixed and treated as inExample I. The phosphor product emits a yellowish-tan when irradiatedwith CR.

EXAMPLE IV The following materials 63.1 g HfO 52.8 g (NH HPO 0.965 g TmO are mixed and treated as in Example I. The phosphor product emits bluewhen irradiated with CR.

EXAMPLE V The following materials:

63.1 g Hf0 52.8 g (NI-1,) I-IPO,

0.880 g EuzOg are mixed and treated as in Example I. The phosphorproduct emits red when excited by 2,537A and 3.650A U.V. and CR.

In the above phosphors, when either terbium or praseodymium is used asan activator, it is recommended that the phosphor be annealed by firingin pure hydrogen for about 6 hours. This annealing step produces aphosphor having a white body color.

It will be seen from the above that there is herein provided a new andnovel family of phosphors having unique characteristics.

While there have been shown and described what are at present consideredthe preferred embodiments of the invention, it will be apparent to thoseskilled in the art that various changes and modifications can be madetherein without departing from the scope of the invention as defined bythe appended claims.

What is claimed is:

1. A phosphor material having the general formula Hf (PO RE wherein REis selected from the group consisting of: terbium, praseodymium;dysprosium; thulium; and europium and is present in an amount of fromabout 0.05 to 0.1 mole per mole of Hf;,(PO

2. The method of making a phosphor material having the general formulaHf (PO RE wherein RE is se' lected from the group consisting of terbium,praseodymium, dysprosium. thulium and europium and is present in anamount of from about 0.05 to 0.10 mole per mole of I-lf ,(PO.,) saidmethod comprising the steps of: forming a substantially homogeneousmixture of a hafnium compound, a phosphate compound and a RE compound inamounts that will yield said phosphor upon subsequent heating; andheating said mixture in an open crucible for about four hours at about1,300C.

3. The method of claim 2 wherein said hafnium compound is HfO 4. Themethod of claim 3 wherein said phosphate compound is (NH, HPO.,.

5. The method of claim 4 wherein said RE compound is an oxide.

1. A PHOSPHOR MATERIAL HAVING THE GENERAL FORMULA HF3(PO4)4: RE WHEREINRE IS SELECTED FROM THE GROUP CONSISTING OF: TERBIUM, PRASEODYMIUM,DYSPROSIUM, THIULIUM, AND EUROPIUM AND IS PRESENT IN AN AMOUNT OF FROMABOUT 0.05 TO 0.1 MOLE PER MOLE OF HF3(PO4)4.
 2. The method of making aphosphor material having the general formula Hf3(PO4)4: RE wherein RE isselected from the group consisting of terbium, praseodymium, dysprosium,thulium and europium and is present in an amount of from about 0.05 to0.10 mole per mole of Hf3(PO4)4 said method comprising the steps of:forming a substantially homogeneous mixture of a hafnium compound, aphosphate compound and a RE compound in amounts that will yield saidphosphor upon subsequent heating; and heating said mixture in an opencrucible for about four hours at about 1, 300*C.
 3. The method of claim2 wherein said hafnium compound is HfO2.
 4. The method of claim 3wherein said phosphate compound is (NH4)2 HPO4.
 5. The method of claim 4wherein said RE compound is an oxide.